Patent Literature 1 discloses a technology concerning a roll body (hereinafter referred to as “roll”) in which a polyolefin microporous film (hereinafter referred to as “microporous film”) is wound around a winding core (hereinafter referred to as “core”). According to the technology disclosed in Patent Literature 1, the microporous film is wound around the core so that an absolute value of a difference between a calculated thickness of the microporous film and an actual thickness of the microporous film is a prescribed value or less, which calculated thickness is calculated based on (i) an outer diameter of the roll, (ii) an outer diameter of the core, and (iii) a length of the microporous film wound around the core. This is believed to configure the roll so that the microporous film is neither loose nor excessively tight.